Field of the Disclosed Technology
This invention relates generally to firearms comprising a bolt having locking lugs. More particularly, this invention relates to improvements in coaxial alignment of components of such a firearm, and preferably also limiting the effect of rain, water, freezing water, snow, ice, dirt, vegetation, and/or other elements entering the firearm in a field environment, for example, during target shooting, hunting, or combat in inclement, uncontrolled, or unclean environments.
Background/Related Art
Firearms having an action comprising a bolt with locking lugs are well-known and may feature different types of bolt actuation, for example, bolt-handle action, lever action, pump action, automatic action, and semi-automatic action. Conventionally, there has been a compromise in the design of such firearms between accuracy and tolerance to elements that may enter and interfere with the firearm action. A key to accuracy is to have the bullet travel straight down the firearm barrel and exit the muzzle pointing the same direction the barrel was pointed when the trigger was pulled. One or more misalignments may be responsible for inaccuracy in bullet travel, for example, misalignment of the cartridge in the chamber, misalignment of the barrel bore relative to the bolt and/or receiver, and/or axial-misalignment of threads or an inaccurately-cut radial receiver face for connection of the barrel to the receiver. A combination of multiple of these misalignments tends to create an inaccurate firearm, especially in field firearms that are made with loose tolerances to allow movement and cycling of the action in spite of interference by elements present in outdoor or other non-controlled/non-clean environments. For example, for precision rifle shooting, compromise in rifle design typically makes a rifle either more accurate but less usable in the field (a “benchrest rifle”), or more usable and tolerant to dirt and weather but not as accurate (a “field rifle”).
Benchrest rifles have such tight tolerances that they don't work well with dirt and weather encountered in the field and require frequent cleaning after only one or a few rounds are fired, but they are consistently more accurate. Additionally, benchrest rifles are usually impractical in the field due to their weight. The components of benchrest rifles are built heavier to resist flexing that causes harmonic vibrations, which can cause inaccuracy. For example, benchrest barrels are built heavier to reduce barrel whip when the round is fired.
Field rifles have relatively loose tolerances between moving components, because loose tolerances allow ice and dirt to be present without limiting operability of the action, and also permit less expensive manufacture. Field rifles, with thinner components and barrels, are also much lighter for being carried about in rough field terrain.
The patent literature illustrates attempts to increase accuracy of bolt-action firearms. U.S. Pat. No. 6,209,249 Borden discloses a bolt for a firearm with increased accuracy. The bolt body has front and rear exterior bosses with diameters slightly larger than the rest of the bolt body, resulting in a tighter tolerance between portions of the bolt and the bolt runway in the regions of the bosses. U.S. Pat. No. 7,975,417 Duplessis et al. discloses joining a barrel to the receiver of a bolt-action rifle with a threaded insert. The Duplessis, et al. threaded insert may be considered a separate, trunnion piece that helps set the rifle headspace, to offset/account for barrel machining error, and that helps with barrel interchangeability.
Custom rifle manufacturers have made some improvements, or have pushed the boundaries of turning a conventional field rifle into a more accurate long-range rifle, by reducing the tolerances between the bolt body and the bolt bore of the receiver of the rifle thereby reducing bolt and cartridge misalignment. Instead of the approximately 0.015 (fifteen thousandths) inch clearance between the bolt and the receiver in many field rifles of the past, these custom manufacturers often make the clearance approximately 0.005 (five thousandths) inch. Reducing this clearance makes the bolt better aligned with the receiver. This compromise, however, makes the rifle action more susceptible than a field rifle to binding and blockage from outdoor interferences such as dirt and ice, and makes the rifle still not as accurate as a benchrest gun that often has approximately 0.0005 (five ten-thousandths) inch clearance.
A BORDEN™ rifle action has very tight tolerances between the receiver and the bolt bosses that are behind the bolt lugs, specifically, approximately 0.0005 (five ten-thousandths) inch, starting from when the bolt starts to enter lock up (the beginning of the rotation), all through the approximate 90 degree rotational turn into the “locked-up” (also, “battery”) position. The bolt bosses are what have been called “BORDEN™ bumps”, which are in the bolt body that lie behind (proximal to) the bolt lugs and in front of (distal to) the bolt handle. These bosses have a larger maximum diameter than the bolt body, serving the purpose of reducing clearance between the bolt and the receiver bore in the location of the bosses. Such bosses, however, are behind (proximal to) the bolt lugs, and are susceptible to binding and blockage when outdoor interferences such as dirt and ice enter between the bolt bosses and the receiver bore. Thus, the BORDEN design relies on precise manufacture of the portions of the bolt main body and the receiver that are behind (proximal to) the bolt lugs and behind (proximal to) the lug abutments/stops, respectively. That is, the BORDEN design relies on precise manufacture of structure/surfaces that are separate, and distant, from the bolt lugs, bolt distal face, and the barrel threaded connection to the receiver.
Therefore, there is still a need to provide more shooting accuracy in a “field-capable” firearm that has an action comprising a bolt with locking lugs. Therefore, an object of certain embodiments is to improve axial alignment of the bolt, cartridge, receiver, and barrel, of such a firearm, for increased shooting accuracy. An object of certain embodiments is to accomplish said improved axial alignment by specially-adapting the distal end of the receiver forward of the lug stops, and preferably also the distal end of the bolt at the lugs and the proximal end of the barrel where it connects to the distal end of the receiver. An object of certain embodiments is to accomplish said axial alignment by having the lugs when in their locked condition, and also a barrel axial surface, mate with the same surface, for example, with adjacent portions of the same surface. An object of certain embodiments is to achieve said improved axial alignment while achieving consistent operability of said axial alignment in the adverse conditions experienced in field environments, including outdoor hunting and combat environments, and other non-pristine environments/conditions. An object of certain embodiments is to provide a firearm that shoots with near-benchrest accuracy, but that tolerates build-up of dirt, ice, water, or other interfering elements on moving parts, without undue binding or blockage and the resulting excessive mechanical failure of the moving parts. An object of certain embodiments is to accomplish said tolerance of interfering elements by means of the lug having a debris-cleaning/scraping capability. An object of certain embodiments is to achieve said improved axial alignment by means and methods that also reduce machining steps and also reduce or eliminate hand-tooling and customizing of the shape and length of each rifle barrel firing chamber/head-space. An object of certain embodiments is to provide a field-capable firearm that is accurate in spite of imperfections in the firing chamber/headspace shape or surfaces and in the cartridge casings, and/or the imperfections from fouling of the firing chamber/headspace surfaces that are intended to align the distal shoulder of the casing. Certain embodiments of the invention meet or exceed one or more of these objects, as will be further understood from the following discussion.